Implantable neurostimulation systems generate electrical stimuli to body nerves and tissues for the therapy of biological disorders, such as Spinal Cord Stimulation Systems to treat chronic pain, Cochlear Stimulation Systems to treat deafness, and Deep Brain Stimulation Systems to treat motor and psychological disorders, etc. All of the implantable stimulation systems need energy to operate and generate stimulation. The energy usually comes from an external power source or from an implanted battery. For neurostimulation systems powered by the external device, an external power device is needed to be continuously worn to power the implanted devices. Some neurostimulation systems utilize an implanted battery to provide power for stimulation. An example of one such neurostimulation system is disclosed in U.S. Pat. No. 6,516,227. The rechargeable spinal cord stimulation system with an implanted lithium-ion battery achieves longer operation lifetime and smaller device size. The implanted battery needs to be recharged occasionally to maintain sufficient energy to power the stimulation electronic circuitry. In U.S. Pat. No. 6,516,227, an off-the-shelf, linear regulation battery charger integrated circuit (IC) available from Linear Technology as part number LTC1731-4.1 is used to receive power through inductive coupling from an external charging system and to provide proper charge current and voltage for the battery.
In addition, as described in U.S. Pat. No. 6,516,227, if the battery has been discharged below a certain voltage level or completely discharged to zero volts, the rechargeable spinal cord stimulation system will temporarily shut off the stimulation. It may take up to two hours to charge the battery to a capacity that allows stimulation to be resumed again. This means patients may have to wait some time until the battery is charged enough to provide stimulation again.
U.S. Pat. No. 5,769,877 discloses an implantable device with a capacitive replenishable power source that is able to replenish and simultaneously deliver stimulating pulses to targeted tissues.
U.S. Pat. No. 6,272,382 discloses a fully implantable cochlear stimulator (ICS) system with an implanted rechargeable battery and an external battery charger (EBC). As described in this patent, in the event the implanted battery within the implantable speech processor (ISP) module malfunctions, or for whatever reason cannot be used, or the user or clinician (or other medical personnel) does not want to use it, it is still possible, through use of the EBC to provide operating power to the ISP module and ICS module so that they may continue to function for their intended purpose (e.g., stimulating and/or sensing). By having such a backup option available, the patient may delay battery-replacement and/or corrective surgery indefinitely.
U.S. Pat. No. 6,826,430 discloses a fully implantable cochlear prosthesis that includes an implantable housing with a charger 33. As described in this patent, an RF coil 30 receives power and may transmit back telemetry data. The received power is rectified by diode D1 and powers a linear Lithium Ion Battery Charger 33 to charge an implanted battery 34. A Battery Protection Circuit 35 protects the battery from conditions such as over charge and over-discharge, automatically disconnecting the source or load when necessary. The system can still operate from an external source through the coil 30 if the battery is disconnected. A Buck Converter Circuit(s) 36 derives the necessary power supply voltages from the battery voltage that are required for operation of the prosthesis.
It would be desirable to be able to provide a battery charger circuit that permits externally transmitted power to be used for charging an implanted battery and powering a stimulation circuit, and which is controlled by the stimulation circuit and can be used to power the stimulation circuit when the implanted battery is disconnected, defective, or determined to not be suitable for use.
It would further be desirable to be able to provide a battery powered implantable neurostimulation system with a battery charger circuit that is easily integrated with modern integrated circuits technology, such as CMOS N-well integrated circuits technology.
It would further be desirable to be able to provide a battery powered implantable neurostimulation system with a battery charger circuit that is configured to charge an implanted battery depending upon a specification characteristic of the battery.